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Abstract

This text is based on a talk given in September 1994 on the occasion of a golden anniversary reunion held at the University of Sydney School of Physics to commemorate the six radiophysics courses conducted by the staff of the school for the Australian armed services in the years 1941-1944. The courses were designed as initial training for radar (then called radiolocation) technical officers.
I will discuss interactions between World War II radar and other wartime developments (such as code-cracking devices) and the computer field. I am fortunate in that after almost four wartime years in RAAF ground radar, I have been able to spend most of my subsequent career in the computer field. Most of the first 15 years of that time was spent in the United Kingdom and Australia designing, building, or using computers with memory systems developed from techniques originally devised in a radar context. Also, I worked with a number of engineers and mathematicians who had come to computers from radar development and code-cracking centers.

This text is based on a talk given in September 1994 on the occasion of a golden anniversary
reunion held at the University of Sydney School of Physics to commemorate the six
radiophysics courses conducted by the staff of the school for the Australian armed services in
the years 1941-1944. The courses were designed as initial training for radar (then called
radiolocation) technical officers.

I will discuss interactions between World War II radar and other wartime developments (such as
code-cracking devices) and the computer field. I am fortunate in that after almost four wartime
years in RAAF ground radar, I have been able to spend most of my subsequent career in the
computer field. Most of the first 15 years of that time was spent in the United Kingdom and
Australia designing, building, or using computers with memory systems developed from
techniques originally devised in a radar context. Also, I worked with a number of engineers and
mathematicians who had come to computers from radar development and code-cracking
centers.

Radar

Toward the end of World War II, major radar developments related to MTIs -- moving target
indicators [8]. The movement of targets can be detected by storing reflections from successive
pulses and subtracting them. Noncancellation indicates movement, and separation between two
noncanceling signals is a measure of the movement of a target between successive transmitter
pulses. What is needed is a means of storing echoes from successive pulses and subtracting
them. Storage techniques so devised were later used (in modified form) to store digital
information for computation, two-level (binary) representation being the most convenient.

In its simplest form, a radar transmitter outputs power only during the pulse modulation period.
The Doppler effect, which changes the frequency of electromagnetic radiation reflected from a
moving object, can be exploited by comparing the frequency of the reflected pulse with that of
the transmitted pulse. To do this, some technique is needed for retaining information about the
transmitted pulse carrier phase -- a process that is not possible if the transmitter oscillator
operates only for the duration of the modulating pulse, as is the case, say, with a magnetron
oscillator. However, if the transmitter pulse carrier is generated by amplifying the amplified
output of a klystron during the pulse period, the Doppler effect will result in a frequency shift in
the moving target echo that can be measured by the frequency differences between reflected
echo and the transmitter pulse to give the target velocity with respect to the transmitter. Mixing
with an intermediate frequency -- a long-establi...